1. Field of the Invention
The present invention relates to a wastewater treatment apparatus, and more particularly to a wastewater treatment apparatus that treats wastewater by flocculation and magnetic separation by adding a flocculant and magnetic powder to the wastewater.
2. Description of the Related Art
A water treatment method that uses a flocculation and magnetic separation system obtains treated water by adding a flocculant and magnetic powder to wastewater that is the object of treatment, generating flocculated flocs (hereunder, referred to as “magnetic flocs”) by agitating the resulting mixture, and recovering the magnetic flocs using a magnetic force produced by a magnetic separation apparatus.
According to this method, magnetic flocs that include magnetic powder are recovered, and it is necessary to dispose of the recovered magnetic flocs as industrial waste. Consequently, the cost of supplying magnetic powder and the cost of disposing of the recovered flocs as industrial waste lead to an increase in running costs.
Technology for solving the foregoing problem is known, as disclosed in Japanese Patent Application Laid-Open No. 11-123399 and Japanese Patent Application Laid-Open No. 11-207399, in which sludge containing magnetic powder is decomposed by a hydrothermal reaction and the volume of sludge is reduced.
According to the wastewater treatment apparatuses disclosed in Japanese Patent Application Laid-Open Nos. 11-123399 and 11-207399, sewage is purified by flocculation and magnetic separation using a magnetic separation apparatus, sludge that is generated at that time is hydrothermally treated at a high temperature and a high pressure, and magnetic powder is recovered by magnetic separation in a high-temperature and high-pressure line.
However, according to the wastewater treatment apparatuses disclosed in Japanese Patent Application Laid-Open Nos. 11-123399 and 11-207399, there has been the problem that in order to obtain sufficient floc decomposition performance when subjecting sludge to hydrothermal treatment at a high temperature and a high pressure, not only is a significant amount of energy required, but the structure of the hydrothermal apparatus used for the floc decomposition process also becomes complex. In this connection, according to Japanese Patent Application Laid-Open No. 11-123399, sludge is pressurized to 10 MPa or more and heated to less than 350° C., and thereafter is lead to a magnetic powder separator. According to Japanese Patent Application Laid-Open No. 11-207399, sludge is pressurized to approximately 2 MPa and heated to around 200° C., and thereafter is lead to a magnetic powder separator.